Peptides that are obtainable by hydrolyzing proteins are incorporated into compositions used for hair applications, in expectation of a hair restoring effect or a hair conditioning effect. Also, research and development aimed at an enhancement of the effects of such peptides or addition of functions of such peptides has been carried out, and as a result, cationized, acylated, or silylated peptide derivatives are now known.
JP 2011-144127 A discloses, as a peptide derivative to be incorporated into a hair treatment agent, a modified peptide obtainable by introducing a carboxymethyl disulfide group into a peptide using a thioglycolate. It is considered that when this modified peptide is used, a restoring effect in the hair can be expected.
Furthermore, JP 2012-056855 A discloses a modified peptide having a carboxyl group as an introduced group, which is obtainable using a thioglycolate, a thiolactate, or a thiomalate.